Six months after the Sri Lankan Government won its war with the Tamil Tigers, allegations are surfacing of war crimes committed in the final months of the conflict.

Last month the US Department of Homeland Security tried to question the Sri Lankan presidential candidate and US citizen, General Sarath Fonseka, about possible war crimes.

But the Australian Government has made no such moves to question a prominent dual Sri Lankan-Australian citizen about his activities.

In the last days of the civil war, it is alleged two political leaders of the rebel Tamil Tiger fighters were killed as they tried to lay down their arms and surrender.

The men led about a dozen men and women under a white flag to waiting Sri Lankan army troops.

A Tamil eyewitness said the soldiers fired on them with machine guns. Everyone in the group was killed.

The incident is mentioned in a 2009 US State Department report to Congress, on possible violations of international humanitarian law in Sri Lanka, from January until the end of May this year.

The report says "the leaders, Nadesan and Puleedevan, spoke to international and domestic figures, who acted as intermediaries with the then foreign secretary, Dr Palitha Kohona, to negotiate a surrender. Nadesan requested a UN witness but was told he had the Sri Lankan President's guarantee of safety".

Dr Kohona is now Sri Lanka's ambassador to the United Nations. He is also an Australian citizen and, according to Hansard, a former senior official with the Department of Foreign Affairs and Trade.

When asked what his role was in arranging the surrender, he told the ABC he had "no role in arranging anything".

"Because I was in foreign ministry I had nothing to do with the defence ministry or the defence forces, and I don't think anything was arranged anyway," he said.

"I don't think anybody else was involved in such a surrender either.

"There was an attempt to wake me up in the middle of the night, and I told them that I was not the person to contact about those demands.

"There was a general query about surrendering and I told them that I was the wrong person, that I had nothing to do with surrendering and asked them to go and deal with the matter in the way it ought to be dealt with."

Three weeks after the shooting, Sri Lanka's army chief General Sarath Fonseka was reported as saying the military had to overlook traditional rules of war and kill Tamil Tiger rebels who had come under white flags to surrender.

Calls for an investigation

Don Rothwell, professor of international law at the Australian National University, says as a diplomat Dr Kohona has immunity from prosecution, but recently international law courts have begun to question this principle in the case of possible war crimes.

"There's nothing to suggest Dr Kohona was directly responsible for committing these alleged war crimes, though international law does recognise principles of what's called command responsibility, where if someone had direct command, whether it's legal or political, with respect to the commission of these types of offences," he said.

Mr Rothwell says in this case, there is enough material to launch a preliminary investigation.

"Dr Kohona is a dual Australian-Sri Lankan citizen. The fact that he is an Australian citizen automatically activates obligations for Australia to investigate this matter at the legal level, but the fact that he was a former high-profile official for the Australian Government representing Australia in international negotiations, I think perhaps places an even stronger responsibility on Australia to at least conduct the initial investigations into this matter," he said.

Mr Kohona says the allegations "first and foremost ... need to be substantiated [and] no country goes around investigating silly accusations based on innuendo and unsubstantiated facts".

Both the Federal Government and the Australian Federal Police (AFP) say they are aware of the US State Department's report.

The AFP says it has not received any referral to investigate Dr Kohona for alleged war crimes.

A spokesman for the Attorney-General's Department says investigation and prosecution by the country in which criminal conduct occurred is the most appropriate way to bring an alleged war criminal to justice.